February 8, 2012

Earth's glaciers and ice caps outside of the regions of Greenland and Antarctica are shedding roughly 150 billion tons of ice annually, according to a new study led by the University of Colorado Boulder.

The research effort is the first comprehensive satellite study of the contribution of the world's melting glaciers and ice caps to global sea level rise and indicates they are adding roughly 0.4 millimeters annually, said CU-Boulder physics Professor John Wahr, who helped lead the study. The measurements are important because the melting of the world's glaciers and ice caps, along with Greenland and Antarctica, pose the greatest threat to sea level increases in the future, Wahr said.

The researchers used satellite measurements taken with the Gravity Recovery and Climate Experiment, or GRACE, a joint effort of NASA and Germany, to calculate that the world's glaciers and ice caps had lost about 148 billion tons, or about 39 cubic miles of ice annually from 2003 to 2010. The total does not count the mass from individual glacier and ice caps on the fringes of the Greenland and Antarctic ice sheets -- roughly an additional 80 billion tons.

"This is the first time anyone has looked at all of the mass loss from all of Earth's glaciers and ice caps with GRACE," said Wahr. "The Earth is losing an incredible amount of ice to the oceans annually, and these new results will help us answer important questions in terms of both sea rise and how the planet's cold regions are responding to global change."

Changes in ice thickness (in centimeters per year) during 2003-2010 as measured by NASA's Gravity Recovery and Climate Experiment (GRACE) satellites, averaged over each of the world's ice caps and glacier systems outside of Greenland and Antarctica. Credit: NASA/JPL-Caltech/University of Colorado

A paper on the subject is being published in the Feb. 9 online edition of the journal Nature. The first author, Thomas Jacob, did his research at CU-Boulder and is now at the Bureau de Recherches Géologiques et Minières, in Orléans, France. Other paper co-authors include Professor Tad Pfeffer of CU-Boulder's Institute of Arctic and Alpine Research and Sean Swenson, a former CU-Boulder physics doctoral student who is now a researcher at the National Center for Atmospheric Research in Boulder.

"The strength of GRACE is that it sees everything in the system," said Wahr. "Even though we don't have the resolution to look at individual glaciers, GRACE has proven to be an exceptional tool." Traditional estimates of Earth's ice caps and glaciers have been made using ground-based measurements from relatively few glaciers to infer what all of the unmonitored glaciers around the world were doing, he said. Only a few hundred of the roughly 200,000 glaciers worldwide have been monitored for a decade or more.

Launched in 2002, two GRACE satellites whip around Earth in tandem 16 times a day at an altitude of about 300 miles, sensing subtle variations in Earth's mass and gravitational pull. Separated by roughly 135 miles, the satellites measure changes in Earth's gravity field caused by regional changes in the planet's mass, including ice sheets, oceans and water stored in the soil and in underground aquifers.

A positive change in gravity during a satellite approach over Greenland, for example, tugs the lead GRACE satellite away from the trailing satellite, speeding it up and increasing the distance between the two. As the satellites straddle Greenland, the front satellite slows down and the trailing satellite speeds up. A sensitive ranging system allows researchers to measure the distance of the two satellites down to as small as 1 micron -- about 1/100 the width of a human hair -- and to calculate ice and water amounts from particular regions of interest around the globe using their gravity fields.

For the global glaciers and ice cap measurements, the study authors created separate "mascons," large, ice-covered regions of Earth of various ovate-type shapes. Jacob and Wahr blanketed 20 regions of Earth with 175 mascons and calculated the estimated mass balance for each mascon.

The CU-led team also used GRACE data to calculate that the ice loss from both Greenland and Antarctica, including their peripheral ice caps and glaciers, was roughly 385 billion tons of ice annually. The total mass ice loss from Greenland, Antarctica and all Earth's glaciers and ice caps from 2003 to 2010 was about 1,000 cubic miles, about eight times the water volume of Lake Erie, said Wahr.

"The total amount of ice lost to Earth's oceans from 2003 to 2010 would cover the entire United States in about 1 and one-half feet of water," said Wahr, also a fellow at the CU-headquartered Cooperative Institute for Research in Environmental Sciences.

The vast majority of climate scientists agree that human activities like pumping huge amounts of greenhouse gases in the atmosphere is warming the planet, an effect that is most pronounced in the polar regions.

One unexpected study result from GRACE was that the estimated ice loss from high Asia mountains -- including ranges like the Himalaya, the Pamir and the Tien Shan -- was only about 4 billion tons of ice annually. Some previous ground-based estimates of ice loss in the high Asia mountains have ranged up to 50 billion tons annually, Wahr said.

"The GRACE results in this region really were a surprise," said Wahr. "One possible explanation is that previous estimates were based on measurements taken primarily from some of the lower, more accessible glaciers in Asia and were extrapolated to infer the behavior of higher glaciers. But unlike the lower glaciers, many of the high glaciers would still be too cold to lose mass even in the presence of atmospheric warming."

"What is still not clear is how these rates of melt may increase and how rapidly glaciers may shrink in the coming decades," said Pfeffer, also a professor in CU-Boulder's civil, environmental and architectural engineering department. "That makes it hard to project into the future."

According to the GRACE data, total sea level rise from all land-based ice on Earth including Greenland and Antarctica was roughly 1.5 millimeters per year annually or about 12 millimeters, or one-half inch, from 2003 to 2010, said Wahr. The sea rise amount does include the expansion of water due to warming, which is the second key sea-rise component and is roughly equal to melt totals, he said.

"One big question is how sea level rise is going to change in this century," said Pfeffer. "If we could understand the physics more completely and perfect numerical models to simulate all of the processes controlling sea level -- especially glacier and ice sheet changes -- we would have a much better means to make predictions. But we are not quite there yet."

Related Stories

Despite growing public alarm over the shrinking Greenland and Antarctic ice sheets, it is small glaciers and ice caps that have been contributing the most to rising sea levels in recent years, according to a new University ...

Greenland is cold and hot. It's a deep freezer storing 10 percent of Earth's ice and a subject of fevered debate. If something should melt all that ice, global sea level could rise as much as 7 meters (23 feet). Greenland ...

(PhysOrg.com) -- Ice loss from the Greenland ice sheet, which has been increasing during the past decade over its southern region, is now moving up its northwest coast, according to a new international study.

(PhysOrg.com) -- The Greenland and Antarctic ice sheets are losing mass at an accelerating pace, according to a new NASA-funded satellite study. The findings of the study -- the longest to date of changes in polar ice sheet ...

(PhysOrg.com) -- The work of Faculty of Science PhD graduate Alex Gardner -- published in Nature magazine in April -- has revealed some alarming evidence that Canada's Arctic glaciers and ice caps have lost nearly as much ...

Recommended for you

At the end of the Pleistocene period, approximately 12,800 years ago—give or take a few centuries—a cosmic impact triggered an abrupt cooling episode that earth scientists refer to as the Younger Dryas.

In a new assessment of nine state-of-the-art climate model simulations provided by major international modeling centers, Michael Rawlins at the University of Massachusetts Amherst and colleagues found broad disagreement in ...

New research confirms that the land under the Chesapeake Bay is sinking rapidly and projects that Washington, D.C., could drop by six or more inches in the next century—adding to the problems of sea-level rise.

The world's deserts may be storing some of the climate-changing carbon dioxide emitted by human activities, a new study suggests. Massive aquifers underneath deserts could hold more carbon than all the plants on land, according ...

Wildfires in California's fabled Sierra Nevada mountain range are increasingly burning high-elevation forests, which historically have seldom burned, reports a team of researchers led by the John Muir Institute of the Environment ...

I think an interesting hypothesis to check is whether high-altitude Asian glaciers might gain mass as a result of global climate change, rather than lose mass.

They might, if precipitation increases in that area of the world.

Why would precipitation increase? Because with rising sea temperatures (and less polar ice in summers), you get more evaporation; and with rising air temperatures, the air can hold more water vapor. Where that precipitation will fall is the big question.

You are correct in the short term, but the long term is probably not the case.

Ridiculously tall mountains like Everest extend above most of the lower troposphere, so they are also not even as heavily impacted by denser greenhouse gases, like CO2.

Just because a region or a mountain lags behind the curve doesn't mean it's permanently safe.

Greenland is already melting, and if it had a higher surface to volume ratio it would probably melt faster. So it lags behind compared to a thinner, flatter ice sheet such as the sea ice. It may take another 5 to 10 years or more before the melt rates start to really kick in for the ice caps.

There are things other than ice which can affect mass measurements. The map shows mass loss in the planes below the glaciers where there isn't any ice. But there is ground water being pumped out for irrigation. If as much ice were melting as claimed it would stand out clearly in the sea level measurements. Even if all this ice was missing, an equally valid theory would be sublimation from cooler, drier temperatures.

You might want to actually ask what skeptics have to say before you pronounce them to have been silenced by a new flavor of the month paper. Otherwise you come off like zero-point energy proponents who keep claiming that scientists are baffled by their knowledge and are "deniers" because they are in the pockets of big oil.

Sean W, where does it say anything about mass loss other than that of glacial mass loss anywhere in the article? Skeptics have a legitemate "one off" answer for every climate change observation we make. It's like someone being infected with a virus that has 25 symptoms 9 out of 10 doctors in the room recognize as symptoms of infection by the virus, and one doctor comes up with 25 different things the patient MAY be infected with based on each indidual symptom....think big picture and give it a rest.

@Sean_W: Pumping groundwater for irrigation could have that effect. BUT TAKE A GOOD LOOK AT THE MAIN MAP. I don't think that there's much pumping of ground water on Baffin Island, or in southern Alaska, Iceland or southern Patagonia, and these are the main regions of loss.

What's completely missing in this article is any comparison. The sensational message of "billions of tons" then in the article quantified to be "that the world's glaciers and ice caps had lost about 148 billion tons" annually, cannot be evaluated without telling us how much the total ice mass on earth is.

In other words, what fraction of the total has been lost in those years, and more importantly, is this trend continuing?

Statements like "The Earth is losing an incredible amount of ice to the oceans annually" are completely meaningless and are scare mongering, without any reference to the total mass of ice that is stored up in the glaciers being evaluated.

"If we could understand the physics more completely and perfect numerical models to simulate all of the processes controlling sea level -- especially glacier and ice sheet changes -- we would have a much better means to make predictions."

In other words, what fraction of the total has been lost in those years

What sort of information would that convey? The point is that- sea levels are rising to a point where we will either have to invest trillions into fortifying coastal cities and island nations or abandoning them altogether (spending trillions to rebuild elsewhere).- even a small rise in sea levels will increase the chance of coastal floods substantially- glacial ice is a major source of fresh water. If glaciers continually lose more than they gain during winter then it's game over for many agricultural areas (and also for many cities along rivers). What this means you can probably imagine.

The point is that- sea levels are rising to a point where we will either have to invest trillions into fortifying coastal cities and island nations or abandoning them altogether (spending trillions to rebuild elsewhere).- even a small rise in sea levels will increase the chance of coastal floods substantially

What database can I go to in order to find a rise in sea levels in recent years?

I do know that all the ice that has melted in the Arctic Ocean in recent years has a net negative effect on ocean levels due to 10% volume shrinkage when ice in water melts to water. But all this stuff melting on land & not reforming as ice somewhere else is of great concern. With all this ice melt overcovering a land mass, there must be associated data showing recent rises in ocean levels.

@Benni - when FLOATING ice melts it has essentially NO EFFECT on sea level. The same percentage of ice is above water level as the amount ice shrinks upon melting, so the shrinkage in melting is offset by all the resulting water being below the water line.

(The effects from the fresh water slightly diluting the sea water and sea water's density not quite being linear with salt content are tiny and can be ignored when discussing global sea-level rise from melting ice).

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.